1. Field of the Invention
This invention relates to a tape cassette, and more particularly to a tape cassette which has a lid and a lock and lock-release mechanism thereof.
2. Description of the Prior Art
A conventional tape cassette such as BETA-type or VHS-type cassette has a tape, a casing consisting of upper and lower shells assembled to each other so as to enclose the tape, and a lid connected to the casing so as to protect the surface of magnetic layer of the tape from dust or dirt during nonuse. The lid has a front plate and to side plates elongated from the front plate form a body. On the other hand, recesses are formed on the outside surfaces of the side walls of the shells so as to receive the side plate of the lid. The lid is rotatably supported at its side plate on the side walls of the shells so as to be closed and locked during nonuse and to be released and unlocked when the cassette is used.
Such a conventional tape cassette is further provided with a tape threading area for drawing out the tape from the cassette casing at the front portion thereof and tape guides for restricting the tape path in the cassette during tape running.
Since the tape path in the cassette is restricted by the tape guides, and the tape threading area is relatively small in the conventional tape cassette, the space near the inside of the side plate of the lid is so efficiently utilized that a lock and lock-release mechanism of the lid is stored therein.
It is, however, desirable to remove the tape guides, since the tape guides directly influence the tape path according to its degree of verticality and causes demagnetization of the tape.
In order to increase the freeness of tape loading system of magnetic recording and/or reproducing apparatus (refered to hereafter as VTR), the threading area formed in the front side of the tape cassette is required to be as large as possible.
Recently, a small-sized tape cassette which is so called 8 mm video cassette has been introduced and is constructed so as to satisfied the condition as described above.
In the 8 mm video cassette, an engaging projection is formed on the inside surface of one of the side plates of the lid at a location behind the rotating axis of the lid. A lid lock lever, which has a corresponding projection to be engaged with the projection of the lid, is provided between the outside of the side wall of the casing and the inside of the side plate of the lid. The lid lock lever is rotatably and resiliently clockwise forced and when the lid is closed, the projection of the lid lock lever is engaged with the projection of the lid so as to lock the lid.
When the cassette is inserted into the VTR, a releasing lever provided within the VTR penetrates between the side plate of the lid and the side wall of the casing. Then the releasing lever hits the lid lock lever so as to rotate the lock lever anti-clockwise against the resilient enforcing power, after the projection of the lock lever is released from the projection of the side plate of the lid.
The lock mechanism of the above described configuration has a defect that the insertion stroke of the releasing lever is long.
A series of compatible cassettes are recently proposed, in which each of the cassettes includes a magnetic tape of the same width, and the tape reels having flanges of different diameter and casing of different dimensions corresponding to the length of the tape.
Namely, a short-length tape is provided into a small-sized cassette, a medium-length tape into a medium-sized cassette and a long-length tape into a large-sized cassette. In order to keep compatibility, the cassette of every size has the threading area formed in same shape at the center of the front portion of the casing.
In such a series of cassettes which are different from each other in the cassette size, however, since the releasing lever for the lid lock lever of the small-sized cassette comes is located under the reel flange of a large-sized cassette, it is difficult to adopt the construction as above described.